The present invention relates to novel thermoplastic polyimide, novel polyamide acid being precursor of the thermoplastic polyimide, and novel thermally fusible laminated film particularly suited for covering electric wires by way of incorporating layer of welding agent comprising the novel thermoplastic polyimide. More particularly, the invention relates to novel thermoplastic composition featuring solid adhesive property under low temperature and solid resistivity to radioactive rays, and yet, the invention relates to novel polyamide acid being precursor of the thermoplastic polyimide composition and novel thermally fusible laminated film particularly suited for covering conductive wires by way of featuring satisfactory workability, softness, and solid adhesive property. In particular, the novel thermally fusible laminated film exerts distinct resistivity to radioactive rays.
Owing to solid thermal resistant property, satisfactory physical properties under low temperature, durable resistance against chemicals, and satisfactory electrical characteristic, polyimide film has widely been used for composing a variety of components built in electric and electronic apparatuses. However, since polyimide conventionally being used in the form of film is generally insoluble and infusible, in the course of enveloping metallic wires with polyimide film, normally, resinous layers having thermal fusibility are laminated on the polyimide film.
On the other hand, as a result of significant development of modern physics in the field of element particles in recent years, construction of improved accelerators has been promoted to generate higher energy. In order to securely generate higher energy, it is imperative for all the concerned to generate extremely intense magnetic field by means of those magnets capable of receiving and transmitting enormous electric current. Recently, many examples are cited regarding the use of superconductive magnets incorporating superconductive wires. In many cases, oxide mainly comprising copper is used for composing superconductive wires. However, when using adhesive agent made from thermosetting resin to cover the superconductive wires with insulated covering material, after executing a thermal treatment, proportion of oxide components in the superconductive wires is easily variable to result in the degraded physical properties of the superconductive magnets. To prevent this, it is imperative for the concerned to use such an adhesive agent that securely cures itself and adheres to the superconductive wires under low temperature.
Initially, the above-cited accelerator accelerates movement of elementary particles comprising protons/protons and electrons/electrons to cause them to collide with each other and collapse themselves before investigating particles generated therefrom. Therefore, as a matter of course, an enormous amount of radioactive rays are generated therefrom. Because of this reason, it is imperative that insulated covering material and superficially applied adhesive agent sharing part of the superconductive magnet be extremely resistive to radioactive rays.
Conventionally, in order to properly cover superconductive wires serving under extremely low temperature, such a covering material composed of layers of thermosetting resin mainly comprising epoxy resin laminated on a polyimide film has been used. However, in this case, in order to cure epoxy resin, high temperature is compulsorily applied for a long period of time to cause superconductive wires to unavoidably incur degradation. Furthermore, epoxy resin cannot fully resist radioactive rays, and yet, in anticipation that a greater amount of radioactive rays will be generated in proportion to expansion of the capacity of accelerators, an early development of more effective adhesive agent capable of exerting sufficient adhesion under extremely low temperature and full resistivity against radioactive rays has long been desired.
To solve those technical problems cited above, using such adhesive agent capable of curing itself under extremely low temperature, superconductive wires can be prevented from incurring unwanted degradation. On the other hand, since this adhesive agent quickly cures itself in normal temperature, shell life of this adhesive agent in B-stage is so short that this adhesive agent cannot commercially be offered for use in the form of laminated film.